Fig. 1. A single-engine fighter from an IAI concept drawing, dating back to 1973

– at a time when the Kfir was still under development. This and other IAI

concept studies were described in detail by: S. Tsach and A. Peled, in

Proceedings of the 16th

ICAS.

Fig. 2. Another IAI single-engine concept sketch – this one dating from 1974.

The influence of IAI’s Kfir experience is obvious.

© 2016 by John Golan

Fig. 3. By the mid-1970s, much of IAI’s attention had turned towards twin-engine

fighter studies. The concept shown above was labeled as Layout 26.

Fig. 4. The concept shown here is Layout 34. This configuration shared the wing

geometry of the early Layout 33 studies, but with an axisymmetric, supersonic

inlet.

Figs. 5 and 6. Many of IAI’s concept studies during the mid-1970s were focused

on a large, multirole twin-engine proposal. The configuration shown above and

below represents different phases of the Layout 28 design study, which was the

subject of considerable interest.

Fig. 7. A variation on the early Lavi trade studies featuring side-mounted inlets.

Both the side-mounted and ventral inlet offered low distortion at high angles of

attack, but the ventral inlet proved to be lighter.

Fig. 8. One of the more unusual configurations evaluated was the tail boom

design. Although the configuration had promise, it was heavier than the

conventional alternatives.

Fig. 9. As a percentage of Israel’s GDP, Israeli domestic defense spending

reached its peak following the Yom Kippur War, before declining towards a more

sustainable level. Data assembled form: Central Bureau of Statistics, Defence

Expenditure in Israel: 1950-2009; US Office of Management and Budget, Fiscal

Year 2013 Historical Tables.

Fig. 10. US military aid to Israel had plateaued by the mid-1980s, before

declining during subsequent decades. Assembled from: Sharp, US Foreign Aid to

Israel, CRS Report RL33222.

Control Authority at High Angles of Attack

Fig. 11. At elevated angles of attack, a horizontal tail will become stalled well

before the airplane’s wing. Once this happens, the only restoring moment that the

tail can produce will be through added drag.

Fig. 12. In contrast a canard will retain aerodynamic authority even at very high

angles of attack, allowing it to exert a restoring moment through negative-lift

force.

Canard-Wing Interactions

Fig. 13. In a close-coupled design, the canard tip vortices will energize both the

wing boundary layer, and the wing tip vortices.

Fig. 14. This canard-wing interaction will tend to shift the wing tip vortices

upward, and outward, into a higher energy state. This has the effect of delaying

the onset of vortex break-down, and boundary layer separation, helping to

maintain lift at elevated angles of attack.

Relaxed Static Stability: Conventional Aircraft

Fig. 15. An airplane with a positive static margin will have its aerodynamic center

located behind its center of gravity.

Fig. 16. For a conventional airplane, a small perturbation that increases the angle

of attack will also increase airplane lift, producing a restoring moment.

Fig. 17. The restoring moment due to the increased lift will return a trimmed,

statically stable aircraft to level flight, without direct pilot intervention.

Relaxed Static Stability: Relaxed Static Stability

Fig. 18. An airplane with relaxed static stability will have its aerodynamic center

ahead of the center of gravity, producing a negative static margin.

Fig. 19. A statically unstable airplane will also experience an increase in lift

associated with an increased angle of attack. Only here, the added lift leads to

divergence.

Fig. 20. Without intervention by the flight control software, a statically unstable

aircraft would continue to diverge from level flight.

Subsonic and Supersonic Trim: Conventional Wing and Tail

Fig. 21. In subsonic flight, for a statically unstable aircraft with a conventional

wing and tail arrangement, the horizontal tail would need to exert an upwards trim

force, in order to keep the airplane in level flight. This would enhance the

airplane’s subsonic lift-to-drag ratio.

Fig. 22. In supersonic flight, the aerodynamic center shifts aft, and the airplane

becomes stable. The horizontal tail must now exert a downwards force in order to

trim the airplane, reducing the overall lift-to-drag ratio.

Subsonic and Supersonic Trim: Canard Configuration

Fig. 23. In subsonic flight, the Lavi was expected to rely primarily on elevon

deflection, to provide the trim force necessary to maintain level flight. This

elevon trim force would add to the overall lift of the airplane, and increase its lift-

to-drag ratio.

Fig. 24. In supersonic flight, the Lavi was expected to rely primarily on an

upwards trim force from its canard to sustain level flight. This upwards canard

trim force would enhance the airplane’s supersonic lift-to-drag ratio.

Fig. 25. Composite ply lay-up patterns.

Airplane Tip-Back Criteria

Fig. 26. Good design practice will ensure that the aft-most center-of-gravity will

lie at or near a 15-degree angle from the rear landing gear. This prevents over-

rotation, while also minimizing the control surface hinge moments at take-off.

Turbofan and Turbojet Technology:

The Evolution of Jet Fighter Engines

Fig. 27. The J79, which powered the F-4, Kfir and other aircraft, was among the

last turbojet engines to reach the field.

Fig. 28. Pratt & Whitney’s F100 inaugurated an era of afterburning turbofan

designs that have dominated the jet fighter industry since the 1970s.

The F100 and PW1120: Commonality and Comparison

Fig. 29. The PW1120 shared the same high-temperature core with its F100

predecessor.

Fig. 30. Constraint diagrams illustrate the solution space available for new

designs. The lowest weight alternative, however, that meets all requirements will

invariably be the most affordable.

Fig. 31. A regression line relation for weight estimation – adjusted to match the

Lavi – also turns out to be an excellent predictor for the empty weight of another

dedicated strike jet, once the weight savings from composite technology has been

taken into account.

Hi-Lo-Hi Mission Profile

Fig. 32. Aircraft sizing stems from a combination of performance analyses, and

mission range studies: analyzing fuel burn by breaking the mission down into

small segments.

An Illustrated Look at Range Gate Pull-Off

Fig. 33. The range-gate pull-off technique begins when the airplane’s self-defense

system determines that an enemy radar is actively tracking the airplane

Fig. 34. The electronic countermeasures suite will subsequently broadcast a

mimic signal, with a stronger intensity than the original radar return.

An Illustrated Look at Range Gate Pull-Off

Fig. 35. Gradually, the mimic signal is delayed, so that the tracking radar loses its

fix on the original radar return.

Fig. 36. Finally, the mimic signal is turned off. At this point, the tracking radar’s

“range gate” has completely lost the original radar return, and must re-enter the

search mode to find the target.

Fig. 37. The Lavi Cockpit

Fig. 38. The Lavi was intended to counterbalance its moderate thrust-to-weight ratio with low wing loading.

Fig. 39. Dimensional notations.

Correcting the Oswald Efficiency

Fig. 40. Aerodynamic performance deteriorates as the Mach number increases

Fig. 41. Canard correction factor was calibrated for transonic (Mach 0.90)

conditions.

Fig. 42. The influence of maneuver loads on aerodynamic performance climbs

rapidly as g-load increases, but is less pronounced at transonic Mach numbers –

where performance has already eroded by compressibility effects.

Fig. 43. The E-M Diagram provides a roadmap to jet fighter maneuvering

performance.

Fig. 45. Approximate E-M Diagrams were calibrated to published sustained and instantaneous turn rates for the Lavi

and F-16. Depicted here is the projected E-M Diagram for the Lavi in a lightweight air-to-air configuration at 15,000-ft

altitude, at maximum power.

Fig. 46. Specific excess power for the Lavi is compared to an F-16A in an air-to-air configuration, at maximum power.

Fig. 47. Specific excess power for the Lavi is compared to the MiG-29S in an air-to-air configuration, at maximum

power. The boundaries for the MiG’s envelope became better established following the fall of the Soviet Union – and

subsequent Russian attempts to market the MiG for export.

Fig. 48. Unlike the prior comparisons, this back-to-back study was performed with an external bombload, comparing

the self-defense capability of the Block 30 F-16C to the Lavi. Thrust is set at maximum power.